Hearing assistance devices, such as hearing aids, include, but are not limited to, devices for use in the ear, in the ear canal, completely in the canal, and behind the ear. Such devices have been developed to ameliorate the effects of hearing losses in individuals. Hearing deficiencies can range from deafness to hearing losses where the individual has impairment responding to different frequencies of sound or to being able to differentiate sounds occurring simultaneously. The hearing assistance device in its most elementary form usually provides for auditory correction through the amplification and filtering of sound provided in the environment with the intent that previously inaudible sounds become audible while maintaining comfort for more intense sounds while the device is worn. Hearing aids employ different forms of amplification to achieve improved hearing. However, with improved amplification comes a need for noise reduction techniques to improve the listener's ability to distinguish amplified sounds of interest from those that are classified as noise. Incorporating active noise cancellation (ANC) systems within hearing assistance devices, namely hearing aids, has been documented by several claimants; however, incorporating both technologies is still primitive in its development. Typically, ANC and hearing aids work in opposite ways; hearing aids amplify sound and ANC attenuates sound. However, when combining a hearing aid and an ANC in a suitable way, it is possible to obtain the advantages and technical effects of both systems.
US2012/0250916 and WO2005052911 both relate to a hearing aid which can perform active noise cancellation. In WO2005052911, the hearing aid includes a signal processor which produces a compensation/cancellation signal that can attenuate acoustic signals that bypasses the signal path of the hearing aid and enters the ear canal. In US2012/0250916, the hearing aid includes two microphones and a control unit provided for adjusting a time delay of the two microphone signals.
WO06003618 relates to an earplug with a circuit for active noise cancellation. When a noise signal is received in the earplug, a cancelling signal is processed by means of the circuit to cancel the noise signal. U.S. Pat. No. 6,567,524 teaches a hearing protective earplug with an audio communication terminal for obtaining speech signals of high quality while attenuating noise. The earplug performs noise attenuation automatically adapted to the noise conditions and communication modes. U.S. Pat. Nos. 6,181,801 and 6,021,207 relate to a communications earpiece which receives audio signals, wired and wireless, respectively, sent from an external device such as a mobile phone. Ambient sounds are used for noise cancellation. The communications earpiece can be used by both hearing impaired and non-hearing impaired users.
In an ANC, anti-phasic, but equal amplitude sound is generated in the ear canal in an effort to cause destructive interference and thereby negate the presence of specific sounds. An example would be found in noise cancelling earphones, wherein low frequency, periodic noises like multi-talker babble or aircraft engine noise can be identified, their level and spectral content in the ear canal (or under a headphone) can be captured and analyzed. The phase path to the eardrum predicted, and a signal with equal intensity and frequency composition but 180° out of phase with the ambient sound is added, causing a reduction or elimination of the undesirable sound at the eardrum. However, ANCs typically require a microphone located in the ear canal to capture and analyze the magnitude and phase of the signal, and an algorithm present in the system to allow for the process.